This invention relates to a method of partitioning a particle size distribution diagram of a mixture of several kinds of granular substances having different mean particle sizes, that is, a method of drawing boundary lines between the distributions of respective substances and, especially, to such method using a technique of fuzzy inference in its process.
For example, white blood corpuscles are composed of a mixture of lymph corpuscles, monocytes and granulocytes and its particle size distribution diagram prepared by measuring its particle size and corresponding frequency shows a curve, as shown in FIG. 1, having three peaks A, B and C which correspond respectively to the lymph corpuscle, monocytes and granulocytes. When the number of particles of each substance is counted from this diagram it is necessary to draw partition lines 2 and 4 between the respective peaks to define the regions of respective substances. While these partition lines may be drawn from the bottoms of valleys of the distribution curve as shown, it cannot be done so simply in practice. Because the particle size distribution curve available from a conventional device such as disclosed in U.S. Pat. No. 3,515,884 has undulations as shown in FIG. 2 due to quantizing errors at the time of A/D conversion of measured particle sizes. Such a particle size distribution diagram having undulations often provides a result falling short of an expectaton of experts, when it is input in a computer to seek a position of the minimum frequency. Accordingly, it has been a general practice to execute a smoothing process, such as calculation of a moving average of the data, before patitioning or analyzing the particle size distribution as disclosed in U.S. Pat. No. 4 817 446 for example.
However, it has been impossible to completely remove the undulations by such a smoothing process and, due to such a simple definition of the partitioning position as the minimum frequency position, the above-mentioned problem has been maintained and reproducibility of the result has been very low. For example, if some undulations as shown in FIG. 3 are left in the valley of the distribution curve, the partitioning position of the computer is liable to move within a range R. Although the apparent undulations can be removed completely by enforcing the smoothing process, it is not recommended since the distribution may lose its characteristic feature.
Accordingly, an object of this invention is to provide a novel and improved method which can determine the partitioning position constantly at high reproducibility, using a particle size distribution curve having undulations as described above.